1. Field of the Invention
This invention relates generally to lifting airfoil structures, and more particularly to an airfoil or vehicle spoiler which automatically varies the thickness of the airfoil and therefore proportionately alters the lifting and drag characteristics depending upon the velocity of the air passing over the airfoil.
2. Description of Related Art
Airfoil structures are typically used for creating lift such as in wing, tail and elevator surfaces of an aircraft. The most traditional of these airfoils are fixed, having a top or lifting surface which is longer by virtue of its arcuate configuration than that of the lower surface of the airfoil thus producing lift which enables an aircraft to become airborne and to be maneuvered while in flight.
High speed racing land vehicles also use reverse airfoil structures also known as “spoilers” which produce a downward thrust on the rear portion of the vehicle to increase wheel traction and stability during high speed maneuvering of the vehicle. However, due to the conventional fixed configuration of the spoilers, they can become a bit of a detriment to achieving the vehicle maximum speed and performance due to the fact that the drag produced at higher vehicle speeds will inhibit achieving maximum racing performance of the vehicle.
Considerable effort has been expended in developing airfoil particularly for aircraft flight wherein the airfoil itself may be varied to achieve particular flight characteristics depending upon the speed and maneuvering needs of the aircraft.
U.S. Pat. No. 6,015,115 to Dorsett et al. discloses an aircraft airfoil having inflatable structures to control aircraft. A reconfigurable airfoil is taught by Igram in U.S. Pat. No. 5,004,189.
Riout teaches an improved contoured wing capable of controlled, variable deformation along its profile in U.S. Pat. No. 4,863,117. An airfoil having a relatively thin configuration for high-speed flight and a relatively thick configuration for low-speed flight is disclosed by Krall in U.S. Pat. No. 4,296,900.
U.S. Pat. No. 3,158,338 to Cushman discloses sustaining airfoils having variable configurations to control the lift characteristics of the airfoil. Muscatelli teaches an improved variable airfoil assembly having a fixed airfoil member with a recess in the top for receiving an adjustable airfoil member whose back end is pivoted in U.S. Pat. No. 4,182,503.
A flexible tailored elastic airfoil section is taught by Widnall et al. in U.S. Pat. No. 5,181,678. Ashill et al. teaches an airfoil having a variable geometry expansion surface for the active control of shock strength and transonic wave drag in U.S. Pat. No. 5,433,404.
U.S. Pat. No. 5,531,407 to Austin et al. discloses an apparatus and method for controlling the shape of structures for adaptive wings, hydrodynamic lifting surfaces, submarine hulls and other structures with one or more surfaces and internal actuators. An airfoil having a variable cross section to provide alterable lift characteristics is taught by Rinn et al. in U.S. Pat. No. 6,045,096. Pneumatic adaptive wings are disclosed in U.S. Pat. No. 6,347,769 to To et al.
The present invention, in one embodiment, provides an airfoil which automatically varies in thickness by modifying upper lifting surface of the airfoil responsive to velocity of the airfoil through air. At lower speeds, the airfoil achieves a maximum thickness produced by a biasing member urging the central portion of the lifting surface of the airfoil toward an outwardly-most configuration. However, as air flow increases due to the velocity of the airfoil through air, air pressure against the lifting surface acts against the biasing member to reduce the thickness of the airfoil and thus to reduce the overall lift and correspondingly reduce the air drag of the airfoil at higher speeds.
The foregoing examples of the related art and limitations related therewith are intended to be illustrative and not exclusive. Other limitations of the related art will become apparent to those skilled in the art upon a reading of the specification and a study of the drawings.